Fifty-one North Indian patients with ankylosing spondylitis (AS) are described with mean age of onset 21.2 years and male to female ratio of 16:1. AS began with peripheral arthritis in 47%, low back pain in 41%, acute anterior uveitis in 10%, and heel pain in 2% of the patients. 76% of 51 patients had one of the extra-axial features of AS: peripheral arthritis (61%), heel pain (24%), anterior uveitis (22%), urethritis (12%), kidney disease (10%), mucosal ulcerations (6%), aortic incompetence (4%), and apical pulmonary fibrosis (4%). A majority (71%) of the patients with peripheral arthritis had mono- or oligoarthritis affecting mainly the lower limb joints. Two patients had coexistent rheumatoid arthritis also. HLA-B27 antigen was detected in 48 (94%) of 51 patients compared with 7 (6%) of 118 controls (relative risk 254; Fisher's exact p = 3.49(-29]. On comparing patients with juvenile onset AS and patients with adult onset disease we found peripheral arthritis to be more frequent at the beginning and during the course of disease in the former.